In recent years, as inverter circuits which drive cold-cathode discharge lamps for backlights (hereinafter, simply called discharge lamps) of various kinds of liquid crystal display panels used in liquid crystal TVs, personal computer display surfaces and the like, various kinds of inverter circuits have been known (see, for example, Patent Document 1 described below).
Incidentally, in such an inverter circuit, a resonance frequency f=1/(2π(LC)1/2) which is determined by a secondary side capacity component and an inductance component of the secondary winding of a transformer, which are connected to a discharge lamp in series, becomes an important factor that determines a tube current and efficiency when the inverter is driven. Specifically, for example, in order to drive the inverter circuit with high efficiency, the inverter circuit is preferably operated in the periphery of the resonance frequency, but for this purpose, adjustment of the inductance component of the transformer or the secondary side capacity component is required.
Conventionally, when such resonance frequency adjustment is performed by adjusting the value of the inductance component, the number of windings of the secondary winding of the transformer, for example, is changed. Meanwhile, when the resonance frequency adjustment is performed by adjusting the value of the secondary side capacity component, a capacitor is added to the secondary side high voltage line, for example.
Further, Patent Document 1 described below discloses the one in which the ballast capacitor connected to a discharge lamp is configured by a pattern capacitor. It is naturally possible to form the above described secondary side capacity component by the above described pattern capacitor, and when such a pattern capacitor is used, if the need for adjustment of the above described secondary side capacity component arises, design change of the board is performed in order to make the pattern once again.
Patent Document 1: Japanese Unexamined Patent Publication No. 2005-322479